1. Field of the Invention
The presently disclosed subject matter relates to a wastewater treatment method and a wastewater treatment apparatus, and particularly relates to a method for treating wastewater containing ammonium nitrogen and a treatment apparatus therefor.
2. Description of the Related Art
In recent years, a method including denitrification treatment with the use of anaerobic ammonium-oxidizing bacteria (anaerobic ammonium oxidation method) has drawn attention as a method for treating wastewater containing ammonium nitrogen. This method includes nitriting the ammonium nitrogen in the wastewater into nitrite with nitrifying bacteria in a nitrification tank, and then simultaneously denitrifying the nitrite and the ammonium nitrogen in the wastewater in the denitrification tank with the anaerobic ammonium-oxidizing bacteria. The method does not need the supply of an organic substance from the outside for a denitrification reaction, and accordingly can efficiently perform wastewater treatment.
A simultaneous denitrification reaction in an anaerobic ammonium oxidation method proceeds according to the following reaction formula. Accordingly, in order to reliably decompose and remove the ammonium nitrogen in the wastewater, it is necessary to control the ratio of the ammonium nitrogen and the nitrite nitrogen in the denitrification tank based on the stoichiometric ratio in the following reaction formula. For this reason, the nitrification rate in the nitrification tank has been needed to be strictly controlled.1.00NH4+1.32NO2+0.066HCO3+0.13H+→1.02N2+0.26NO3+0.066CH2O0.5N0.15+2.03H2O
Then, a method (so-called CANON method) is proposed which allows both of the nitrification reaction and the denitrification reaction to proceed in the treatment tank in which the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria coexist, under an aerobic condition (Third, K. A., Sliekers, A. O., Kuenen, J. G., Jetten, M. S. M., 2001 The CANON system (completely autotrophic nitrogen-removal over nitrite) under ammonium, limitation: interaction and competition between three groups of bacteria. Syst. Appl. Microbiol. 24(4), 588-596, for instance). This method can reliably decompose and remove the ammonium nitrogen in the wastewater even without strictly controlling the nitrification rate because the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria which coexist in one treatment tank tend to keep balance with each other.
The CANON method needs to make the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria coexist in one treatment tank. For this reason, a method is proposed which makes both of the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria coexist in one biofilm, and treats the wastewater with the biofilm.
For instance, Japanese Patent Application Laid-Open No. 2001-293494 describes a method of treating wastewater with the use of a carrier (sponge) in which both of the nitrifying bacteria and the anaerobic ammonium-oxidizing bacteria have been immobilized.
In addition, Japanese Patent Application Laid-Open No. 2004-230225 describes a method of preparing a carrier (double-structure carrier) formed of a biofilm with a double structure which has the anaerobic ammonium-oxidizing bacteria entrapped and immobilized therein, and has the nitrifying bacteria attached thereon, and treating wastewater with the use of the carrier.